The calendar may say it's spring, but a major winter-like snow storm is wreaking havoc on the lives of Americans from the Rockies to the Upper Plains. Thirteen states are either under a storm watch or warning.

Nine inches of snow fell on Denver, while Nebraska and the Dakotas expected as much as 2 feet.

Powerful winds ripped the roof off one Harley Davidson store in Pueblo, Colo., and derailed a train off its tracks in Nebraska.

Thick ice was the problem in Sioux Falls, S.D., causing many trees to fall on houses.

Joe Bastardi, chief forecaster at WeatherBell, shared his thoughts on how climate change is impacting weather patters on Newswatch, April 10.

"I thought I heard a very large thunderclap so I thought I'd better go out there and see what's going on and my reaction was 'Oh, my God!'" Sioux Falls resident Sherry Imker said.

The tree that crashed into the roof of the Imker house also damaged their car.

While the Imkers and their neighbors clean up, some scientists are wondering what's happening with the weather. Are we really experiencing global warming? Although greenhouse gases have soared in the past 15 years, air temperatures at the Earth's surface have not.

According to The Economist magazine, 100 billion tons of carbon were added to the atmosphere from 2000 to 2010 -- that's one-fourth of all man-created CO2s put there since 1750.

A NASA scientist reports the five-year mean global temperature has remained flat for the past decade.

While some believe those statistics prove man-made climate change isn't as bad as previously feared, The Economist reports global warming is happening.

Still, skeptics remain unconvinced, including perhaps some of the Americans who are digging out from this week's spring snowstorm.